Measuring and testing – Gas analysis – Detector detail
Reexamination Certificate
2001-06-21
2004-11-09
Cygan, Michael (Department: 2855)
Measuring and testing
Gas analysis
Detector detail
C073S023200, C204S424000
Reexamination Certificate
active
06813930
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a gas sensor utilized for an air-fuel ratio control of an internal combustion engine.
A gas sensor is installed in an exhaust system of an automotive engine for air-fuel ratio control or the like.
A conventional gas sensor comprises a cylindrical insulator having an element insertion hole, a gas sensing element airtightly fixed in the element insertion hole, and a cylindrical housing having an inside space for placing the insulator. An air side cover is attached to a proximal end of the housing so as to confine an aerial atmosphere therein. And, a measured gas side cover is attached to a distal end of the housing so as to confine a measured gas atmosphere therein.
As shown in
FIG. 13
, to facilitate insertion of the gas sensing element
15
, the element insertion hole
210
consists of a larger-diameter portion
211
formed at the proximal end thereof and a smaller-diameter portion
212
formed at the distal end thereof. The larger-diameter portion
211
has an inner diameter larger than that of the smaller-diameter portion
212
.
A sealing material
219
is interposed between an outer surface of the gas sensing element
15
and an inner surface of the larger-diameter portion
211
of the element insertion hole
210
to firmly seal the clearance between them.
The clearance between the gas sensing element
15
and the element insertion hole
210
corresponds to a boundary between the aerial atmosphere and the measured gas atmosphere. It is therefore necessary to airtightly seal the clearance between the gas sensing element
15
and the element insertion hole
210
to surely separate the aerial atmosphere and the measured gas atmosphere.
However, according to the above-described conventional sensor, the smaller-diameter portion
212
is spaced from the gas sensing element
15
via a significant clearance. The gas sensing element
15
is supported at its proximal end with the sealing material
219
in a cantilever fashion.
Accordingly, when a large shock or vibration is applied from the outside, the gas sensing element will swing like a pendulum and may collide with the inner surface of the smaller-diameter portion
212
. Thus, the has sensing element is often subjected to a concentrated stress and broken or damaged.
FIG. 13
shows a portion “A” where the concentrated stress acts to the gas sensing element
15
and a portion “B” where an edged portion of the insulator
21
faces to the gas sensing element
15
. Accordingly, the gas sensing element
15
is often broken at these specific portions.
U.S. Pat. No. 5,886,248 discloses a gas sensor comprising a sealing material provided in a clearance between the gas sensing element and the insulator so as to extend from the proximal end to a distal end thereof.
However, as this sealing material is a hard substance, it has difficulty in preventing the gas sensing element from cracking or breaking when a large shock is applied from the outside, although such a rigid sealing material may be effective against swinging of the gas sensing element.
SUMMARY OF THE INVENTION
To solve the above-described problems, an object of the present invention is to provide a gas sensor which prevents the gas sensing element from cracking and breaking.
To accomplish the above and other related objects, the present invention provides a first gas sensor comprising a cylindrical insulator having an element insertion hole extending from a proximal end to a distal end thereof, a gas sensing element airtightly fixed in the element insertion hole of the insulator, and a cylindrical housing having an inside space for placing the insulator, with an air side cover attached to a proximal end of the housing so as to confine an aerial atmosphere therein and a measured gas side cover attached to a distal end of the housing so as to confine a measured gas atmosphere therein. According to the first gas sensor, a sealing material is provided at one side of the element insertion hole for sealing a clearance between an inner surface of the element insertion hole and an outer surface of the gas sensing element. And, a cushion filler, having the capability of withstanding a loading force ranging from 5N to 1,000N, is provided at the other side of the element insertion hole for sealing a clearance between the inner surface of the element insertion hole and the outer surface of the gas sensing element.
The present invention is characterized in that one end of the gas sensing element is fixed with the sealing material and the other end of the gas sensing element is supported by a soft cushion filler having the strength within the above-described range.
Effects of the present invention will be explained hereinafter.
The cushion filler of the present invention is so soft that it can sufficiently absorb shocks applied from the outside.
Thus, it becomes possible to prevent the gas sensing element from being directly subjected to shocks transmitted from the outside of the gas sensor.
Furthermore, as the gas sensing element of the present invention is held at both of its proximal end and its distal end, the gas sensing element does not swing like a pendulum when it receives shocks or vibrations.
Accordingly, the present invention prevents a concentrated stress from acting on a portion serving as a swing center of the gas sensing element (i.e., a portion immediately below the portion firmly fixed with the sealing material) and also prevents the gas sensing element from colliding with the inner surface of the insulator. Therefore, the present invention effectively prevents the gas sensing element from cracking or breaking.
If the loading force of the cushion filler is less than 5N, insertion of the cushion filler will be difficult. If the loading force of the cushion filler is larger than 1,000N, a large concentrated stress responsive to an external shock will act on the gas sensing element via the cushion filler. This external shock may crack or break the gas sensing element.
In view of facilitating insertion of the cushion filler, it is preferable that the loading force of the cushion filler is equal to or larger than 20N.
Furthermore, the cushion filler can effectively absorb the shock applied from the outside when the loading force of the cushion filler is equal to or less then 400N.
Furthermore, according to the present invention, the clearance between the insulator and the proximal end of the gas sensing element is filled with a dense and hard substance, such as the sealing material. As described previously, the clearance between the gas sensing element and the element insertion hole corresponds to the boundary between the aerial atmosphere and the measured gas atmosphere. Thus, the sealing material interposed between the gas sensing element and the element insertion hole surely separates the aerial atmosphere and the measured gas atmosphere.
As described above, the present invention can provide a gas sensor capable of preventing cracks and breakage of the gas sensing element.
Furthermore, as described later in a preferred embodiment of the present invention, the present invention is applicable to a gas sensor incorporating a multilayered flat plate sensing element and is also applicable to a gas sensor incorporating a cup-shaped solid electrolytic sensing element.
Furthermore, the gas sensor of the present invention is applicable to an air-fuel ratio sensor and to an oxygen sensor installed in an exhaust system of an internal combustion engine, and is also applicable to various sensors, such as a NOx sensor, a CO sensor, and an HC sensor.
The sealing material of the present invention is, for example, glass, talc, steatite, zirconia, and alumina.
The cushion filler of the present invention is, for example, a heat-resistance substance, such as zirconia or ceramic, which has a thermal expansion coefficient similar to that of the insulator or the gas sensing element.
Especially, when the cushion filler of the present invention is used in an exhaust system described in a preferred embodiment, it is subjected to high temperat
Kimata Takehito
Ozawa Masato
Cygan Michael
Nixon & Vanderhye PC
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